Benadryl (diphenhydramine) is a brand-name over-the-counter drug that’s used for allergies and itchy skin. Learn about side effects, price, and more. Learn about the side effects of Benadryl (diphenhydramine), from common to rare, for consumers and healthcare professionals. Benadryl is a brand of various antihistamine medications used to treat allergies, whose content varies in different countries, but which includes some combination of diphenhydramine, acrivastine, or cetirizine. Diphenhydramine, or Diphenylhydramine, sold under the brand name Benadryl among others, is an antihistamine and sedative. Although generally considered sedating, diphenhydramine can cause paradoxical central nervous system stimulation in some individuals, particularly at higher doses. Benadryl is an antihistamine and is used to treat sneezing, runny nose, itching and other allergies. Learn about side effects, interactions and indications. Do you need help relieving allergies or a pesky itch? Check out the many allergy and itch relief products BENADRYL® offers which may help provide relief. Find BENADRYL® dosage information for adults, children, and toddlers and learn how much you and your family should take with our allergy medicine product-dosing guide. Find patient medical information for Diphenhydramine (Benadryl, Unisom, and others) on WebMD including its uses, side effects and safety, interactions, pictures, warnings, and user ratings Benadryl, a common antihistamine, can cause serious side effects like sedation, confusion, and even cardiac arrest, especially at high doses. Understanding these risks is important for safe use. 1 Benadryl (diphenhydramine) is a liquid medication that treats the symptoms of allergies and allergic reactions.